[Bug c++/19448] Different value representation for bitfield width exceeding its type size.

["yanliu at ca dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From yanliu at ca dot ibm dot com  2005-01-14 20:10 -------
You are right, I was using linux and darwin two different compilers. In thse 
two situations, the gcc results are both right. 

I have another question for you for the same testcase: if initializing the 
bitfield with 1, and the bitwidth=17.  I got two different layouts for the 
bitfield member with different g++ compilers:
Both compilers are ppc-rhat. One is 3.4.3, the other is 3.2.3.

Here is the first compiler's info:
Reading specs from /usr/lib/gcc/ppc64-redhat-linux/3.4.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --
infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-
checking --with-system-zlib --enable-__cxa_atexit --disable-libunwind-
exceptions --enable-languages=c,c++,objc,java,f77 --enable-java-awt=gtk --
host=ppc64-redhat-linux --build=ppc64-redhat-linux --target=ppc64-redhat-linux -
-with-cpu=default32
Thread model: posix
gcc version 3.4.3 20041125 (Red Hat 3.4.3-6.EL4)

Running the testcase, here is what I got:
with g++3.2.3, the result is:
Dumping array with size of 4
Character 0 is 0
Character 1 is 1
Character 2 is 0
Character 3 is 0
 c1.m1=1,

With 3.4.3 g++ compiler, the result is:
Dumping array with size of 4
Character 0 is 1
Character 1 is 0
Character 2 is 0
Character 3 is 0
 c1.m1=1,

The Itanium C++ ABI didn't specify how to layout bitfield member if their width 
exceeds its type. Did you put your least-important bit at the left hand side? 
Could you tell me your algorithm on the bitfield member layout? Thanks. 



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19448